This invention relates to compressed air operated brake systems for vehicles and more particularly to systems including one or more spring actuators for applying the brakes through the action of a spring under certain conditions as well as the depletion of said air aiding in pre-trip and D.O.T. regulatory inspection of said system as well as fail safe parking procedures. The Department of Transportation and the National Highway Traffic Safety Administration have regulations requiring the depletion of air pressure on every air brake operated vehicle in order to perform pre-trip inspections of said systems low pressure warning devices before the beginning trip of every day. Also, Department of Transportation officers may require the depletion of said air supply at any time, during any trip, if they wish to perform an inspection of said system. In addition, federal regulations require all school bus drivers to deplete air from the braking system to below approximately 40 p.s.i. every time the vehicle is parked post trip to ensure spring brake application. To date, the standard method of system air depletion used in the field is to repetitively pump or fan the foot brake pedal. This repetitive pumping action must be done until service air pressure is depleted to an air pressure low enough to cause low air pressure actions in the system. The normal operating air pressure of the system is approximately 120 p.s.i. Each pump or fan of the pedal releases approximately 3 p.s.i., therefore it would normally take 26 pumps of the foot brake pedal to effectively deplete the air pressure to necessary p.s.i. This process causes excessive wear on all parts of the braking system every day and every time the process is performed. In addition, as for the parking of air brake commercial vehicles and more particularly school buses, these vehicles do not have a park position on the transmission and places all parking responsibilities on the spring brakes. The primary danger of this process is that as long as the air brake system has a reserve air pressure above approximately 40 p.s.i. the standard push pull parking brake valve can be released by anyone and the vehicle is capable of unwanted and uncontrolled roll off. As a result of this dangerous condition federal guidelines are in place requiring school bus drivers to deplete system air pressure to below 40 p.s.i. every time the vehicle is post-trip parked by fanning the foot brake pedal. This method leaves room for human error of not depleting air pressure to proper p.s.i., as well as afore mentioned wear and tear of entire braking system. As of yet, all other commercial vehicles are not required to deplete system air pressure for final parking which leaves possibly every parked commercial air brake supplied vehicle sitting with the ability of unwanted, uncontrolled roll off. The present invention mechanically depletes the air pressure of said system to proper p.s.i. and achieves low pressure warning system test as well as fail safe parking procedures.